An internal combustion engine typically includes at least one cylinder that receives a piston to form a combustion chamber. The piston is connected to a crankshaft such that a rotation of the crankshaft results in a corresponding reciprocating motion of the piston within the cylinder. Intake and exhaust valves associated with each combustion chamber are indirectly connected to the same crankshaft by way of a timing device such that a rotation of the crankshaft results in corresponding opening and closing movements of the intake and exhaust valves. Thus, the movements of engine valves and the motion of an associated piston, because of their connections to a common crankshaft, are synchronized.
The timing of the opening and closing movements of the intake and exhaust valves relative to the reciprocating motion of the piston may affect performance of the engine. However, this timing of the engine is typically fixed during manufacture of the engine according to a predicted general application of the engine. If operating in a manner other than that predicted by the engine manufacturer, resulting performance of the engine may be less than desired.
In order to maximize the performance of the engine for a particular application, it may be necessary to adjust the relative timing between the movements of the engine valves and the motion of the piston. One method of adjusting this relative timing is described in U.S. Pat. No. 6,532,923 (the '923 patent) issued to Woodward et al. on Mar. 18, 2003. The '923 patent describes varying the typically fixed valve timing of an engine in order to improve combustion. Specifically, the '923 patent discloses an adjustable camshaft sprocket assembly securable to a camshaft that drives intake and exhaust valves. The camshaft sprocket assembly includes a camshaft sprocket driven by a crankshaft and removably securable to a camshaft sprocket hub when the camshaft sprocket assembly is clamped to the camshaft. The camshaft sprocket hub includes a short dowel recess and a long dowel opening offset from the short dowel recess. The camshaft sprocket includes only a long dowel recess. A timing adjustment tool is provided that includes a short dowel, a long dowel, and a handle protrusion. After loosening bolts that axially clamp the camshaft sprocket assembly to the camshaft, the long dowel of the timing adjustment tool is passed through the long dowel opening of the cam sprocket hub into the long dowel recess of the cam sprocket, while the short dowel is inserted only into the short dowel recess of the cam sprocket hub. As torque is applied to the handle protrusion of the timing adjustment tool, the torque is transferred through the engagement of the short and long dowels with the camshaft sprocket and camshaft sprocket hub to generate relative rotation between the two. This relative rotation adjusts an angular orientation between the crankshaft and the camshaft and, thereby, actuation timing of the intake and exhaust valves relative to the motion of an associated piston.
Although the adjustable camshaft sprocket assembly of the '923 patent may improve the combustion process by providing adjustable valve timing, it may be prone to slippage and inaccuracy. In particular, because all torque passing from the camshaft sprocket assembly to the camshaft and visa versa is transmitted only by way of an axial clamping force, it may be possible for rotational slippage to occur between the camshaft sprocket assembly and the camshaft. This slippage could produce inaccurate relative timing that results in undesired performance of the engine and possibly damage to the engine. In addition, because the timing adjustment between the camshaft sprocket assembly and the camshaft is achieved only by a one-to-one ratio of timing adjustment tool rotation to camshaft sprocket assembly rotation, high accuracy of relative timing may be difficult to achieve.
The adjustable valve timing system of the present disclosure solves one or more of the problems set forth above.